1. Field of the Invention
The present invention relates to a planar light source device and a display device using the same, and particularly to a planar light source device having a light guide plate and a display device using the same.
2. Description of Related Art
Some liquid crystal displays use sidelight type (edge light type) planar light source device as a backlight device (backlight unit). In a sidelight type planar light source device, light from a light source enters the side of a light guide plate. Then, the light guide plate emits the light from the light source to the front.
Such sidelight type planar light source device is disclosed (Japanese Unexamined Patent Application Publication Nos. 2001-273807, 2003-162232). In the backlight device disclosed in Japanese Unexamined Patent Application Publication No. 2001-273807, one edge surface of the case to store the light guide plate is bent to form nails. Then, the light guide plate positions the light source unit by these nails.
However, the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2001-273807 does not have enough strength as the light guide plate is supported and fixed only by a case. Accordingly, there is a possibility that the positioned part of the light guide plate may be damaged. In order to realize a planar light source device having a large-sized screen with high luminance especially, it is necessary to increase the number of light sources. Thus the light guide plate must increase its thickness along with that. The thicker the light guide plate, the heavier it becomes. A drop impact causes the light guide plate to be damaged at the positioned part due to the lack of strength in the supporting portion for supporting and fixing the thick light guide plate. When the light guide plate is damaged, there may be luminance unevenness generated in the periphery of the damaged part or the luminance may decrease. Therefore, there is a problem that the performance of the planar light source device will deteriorate. Furthermore, if the extent of breakage is large, it will be necessary to exchange parts.
In the backlight device of Japanese Unexamined Patent Application Publication No. 2003-162232, a concave portion for positioning is formed to the side of a light guide plate. This light guide plate is stored in a frame case. A locking piece is formed in the frame case in the position of the concave portion of the light guide plate. A convex portion is formed in a mold frame in the position of the concave portion of the light guide plate. Then, a locking opening in which the locking piece of the frame case is inserted is formed in the convex portion of the mold frame. Then, the locking piece of the frame case and the locking opening are fitted. Furthermore, an almost horseshoe-shaped bank-like frame is fabricated to the frame case. On the other hand, a horseshoe-shaped groove is formed to the frame of the mold frame. Then, the bank-like frame of the frame case enters into the frame of the mold frame.
However, with the configuration of Japanese Unexamined Patent Application Publication No. 2003-162232, the width of the frame will become large. That is, as the groove is formed in the center of the frame, the width of the frame must be expanded. Moreover, the locking piece of the frame case and the locking opening are fitted. For this reason, the light guide plate is visually recognized in the side surface part of the locking piece. Accordingly, there is a possibility that a large foreign matter may come inside the light guide plate and an optical sheet in a backlight unit. That is, due to the gap between the locking part and the bank-like frame, foreign matters come inside the backlight unit from the gap. Therefore, it is not suitable for the dusty environment. When a foreign matter comes in, there may be luminance unevenness generated and the luminance may decrease. Therefore, there is a problem that the performance of the planar light source device will deteriorate.
The present invention is made against the background of the above situations, and aims to provide a planar light source device with narrow frame and high performance and a display device using the same.